Chemically unrelated tumor promoters induce identical morphological changes in cultured rat oral epithelium

By use of phase contrast microscopy, transmission and scanning electron microscopy the cytomorphological effects of different known tumor promoters (TPA, teleocidin, mezerein and anthralin) were studied and compared to the cytomorphological effects of a variety of non- or weak promoting irritants (ethylphenylpropiolate (EPP), phorbol, acetone, ethanol and dimethyl sulfoxide (DMSO]. The studies were conducted in cultures of stratifying rat tongue epithelial cells. It was demonstrated that the tumor promoters induce characteristic cytomorphological alterations, the most striking changes being elongation of the cells and formation of long cytoplasmic extensions together with induction of so-called "dark cells". The non-promoting irritants exerted well-known cytotoxic reactions like cell rounding and cell sloughing. It is suggested that the characteristic tumor promotor induced cytomorphological effects partly reflects a block of the intercellular communication and thus should be paid more attention as an important characteristic event among the pleiotropic effects exerted by tumor promoters.